Blood Disorders Anemia Hematocrit (HCT) Blood Test What to Expect When Undergoing This Test By Amber J. Tresca Updated on May 04, 2023 Medically reviewed by Steffini Stalos, DO Print Table of Contents View All Table of Contents Purpose of Test How Is the HCT Test Done? Interpreting Results Correcting Abnormal HCT Levels A hematocrit (HCT) test, also known as the packed-cell volume (PCT), measures how much of your blood consists of red blood cells. Red blood cells carry oxygen from your lungs throughout your body. A low HCT could be due to anemia, a vitamin or mineral deficiency, or blood loss. Having too many blood cells could be a sign of dehydration, heart disease, or polycythemia vera (PV). This article explores the purpose of the HCT test, the way in which this simple blood test is done, and how results are interpreted by your healthcare provider. Illustration by Michela Buttignol for Verywell Health Purpose of the HCT Test Red blood cells, also called erythrocytes, are important for distributing oxygen from the lungs to the rest of the body. The percentage of your blood that consists of red blood cells also indicates the (viscosity) thickness of blood. A high or low result on an HCT test can: Be an early indicator of certain conditionsHelp diagnose certain diseasesReflect a response to certain treatments What Other Tests Are Done With HCT? An HCT test is usually ordered as part of a complete blood count (CBC). A CBC provides information on the three major types of blood cells: Red blood cells (RBC) contain an important protein called hemoglobin that carries oxygen so it can be delivered throughout your body. White blood cells (WBC) are part of the immune system and protect our bodies from infection and attack by recognizing bacteria, viruses, and cancer cells. Platelets are responsible for forming clots to stop bleeding and heal wounds. Other tests may be performed at the same time as the HCT test or as a follow-up to help with a diagnosis. These may include: A blood smear: This small blood sample is examined under a microscope for signs of problems. Hemoglobin (Hgb) test: This test measures hemoglobin levels to check for anemia, a blood disorder that's characterized by a low RBC count. When done with an HCT blood test, it is commonly referred to as an H and H test. Iron studies: A group of blood tests, these are interpreted together to check for iron deficiency or iron overload. Reticulocyte count: This blood test that determines how well your bone marrow (the spongy tissue inside bones) makes RBCs. Vitamin B12 and folate levels: This tests to see if you have enough of the nutrients needed to create blood cells. How Is the HCT Test Done? As a basic blood test, the HCT doesn’t require fasting or special considerations. Blood is drawn from the inside of the elbow or the back of the hand. With infants and young children, it may involve a small puncture in the heel or fingertip to collect blood onto a test strip. 7 Tips to Make Getting Blood Drawn Painless How Blood Is Tested Once your blood is collected, it’s placed in a centrifuge or an automated hematology analyzer instrument. The centrifuge separates the red blood cells from the plasma (non-cellular liquid), white blood cells, and platelets, giving a direct measure of the percentage of RBCs in the blood sample. Automated instruments determine the hematocrit (a calculated value) using various methods. Different ways instruments measure/count cells include: Adding fluorescent reagentsElectrical impedance (Coulter principle) Laser beam Whichever method is used, the hematocrit is calculated from the RBC cell count (RBC), mean cell volume (MCV), and the total sample volume (RBC x MCV/10 = Hct). Interpreting Results Age and gender affect hematocrit level, but general guidelines for normal levels in adults and young children are as follows: Age Normal Levels 0 to 3 days 45% to 67% 3 days to 1 week 42% to 66% 1 to 2 weeks 39% to 63% 2 weeks to 1 month 31% to 55% 1 to 2 months 28% to 42% 2 to 6 months 29% to 41% 6 months to 2 years 33% to 39% 2 to 6 years 34% to 40% 6 to 12 years 35% to 45% 12 years to adult (females) 36% to 46% 12 to 18 years (males) 37% to 49% 18 years to adult (males) 41% to 53% HCT test results may be affected by factors such as: DehydrationLiving at a high altitudePregnancyRecent blood transfusion Your healthcare provider will take these factors into account when interpreting the results. If your hematocrit results are outside the normal range, your healthcare provider may have you come in for additional blood tests to help diagnose the cause.Your healthcare provider may want to repeat the HCT test after weeks, months, or at least annually to monitor your levels. Causes of High HCT An above-normal HCT means you have too many red blood cells (polycythemia). Symptoms of high HCT levels include: Bleeding gums Blurred or double vision and blind spotsDizziness or feeling light-headed Fatigue HeadacheHeavy bleeding from small cutsProfuse sweating, especially during sleepSkin symptoms such as itching after a shower or bath, burning, or a red faceShortness of breathVision problems, such as blurred or double vision and blind spotsWeakness High HCT levels are usually caused by an extended period of low oxygen in the blood. It is often a sign of dehydration. However, it may also indicate a more serious health concern, such as: Carbon monoxide poisoning Elevated testosterone levels Heart disease Obstructive sleep apnea Polycythemia vera (PV) or other blood-related diseases Scarring/thickening of the lungs Smoking Causes of Low HCT A low hematocrit number means that your body doesn't have enough red blood cells in your blood. This is also called anemia. Symptoms of anemia include: FatigueHeadachesDizzinessFeeling coldShortness of breath Anemia may be due to the following health conditions: Blood loss due to internal or external trauma Bone marrow damage from chemotherapy or toxins Immune blood disorders, such as Evans syndrome Kidney disease Leukemia, lymphoma, or other bone marrow cancers Nutrient deficiencies, including iron, folate, and vitamins B12 or B6 Too much water in the body Thyroid problems Anemia can also be a side effect of cancer treatments, such as chemotherapy and radiation. Hematocrit results enable healthcare providers to manage anemia if it develops. What HCT Level Is Considered Anemic? For men, an HCT level of less than 41% is considered anemic. For women, that number is slightly lower at less than 36%. The number varies for children depending on their age. Correcting Abnormal HCT Levels If your HCT levels are abnormal, your healthcare provider may order additional tests to identify and treat the underlying cause. For example, if test results point to a bone marrow problem, a bone marrow examination may be needed. A sample of bone marrow is taken, usually from the hip, to check for lymphoma and similar disorders. In addition to treating the underlying cause, your healthcare provider may recommend diet or lifestyle changes, supplements, or medications. How to Increase HCT If your results, along with other tests, indicate that you have iron-deficiency anemia, you can usually improve your red blood cell count by fortifying your diet with iron-rich foods. Some examples of iron-rich foods include: Red meatChickenLiverEggsShrimpTunaSpinachPeasBroccoliWhole wheat breadTofuBeans Your healthcare provider may also suggest taking over-the-counter iron supplements. If iron deficiency anemia is severe, a blood transfusion may be needed. If anemia is the result of a bacterial infection, you may need to begin antibiotics. How to Lower a High HCT If you have a condition that causes overproduction of RBCs, your healthcare provider may suggest lifestyle changes such as quitting smoking or adopting a heart-healthy diet. Sometimes dehydration can cause high hematocrit levels. In this case, drinking lots of fluids can bring your levels back to normal. In the rare case of PV, a healthcare provider can provide medication that will help you manage the condition, but it cannot be cured. Which Foods to Eat When You Have Anemia Summary A hematocrit test gives your healthcare provider important information about your health. The test measures red blood cells, which have a protein that delivers oxygen throughout your body. The HCT test can help to diagnose or monitor blood disorders, dehydration, nutrient deficiencies, blood-related cancers, and many other conditions. If your test results are abnormal, other tests may be performed at the same time or afterward to help identify the cause of anemia (low hematocrit) or high red blood cell counts, so you can get the right treatment. 10 Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. U.S. National Library of Medicine. MedlinePlus. Hematocrit test. Avecilla S, Marionneaux S, Leiva T, et al. Comparison of manual hematocrit determinations versus automated methods for hematopoietic progenitor cell apheresis products. Transfusion. 2016;56(2):528-32. doi: 10.1111%2Ftrf.13346 Seattle Children's Lab. Hematocrit. Mount Sinai. Hemoglobin. U.S. National Library of Medicine. MedlinePlus. Anemia. National Cancer Institute. Anemia: Cancer Treatment Side Effect. American Red Cross. What does hematocrit mean? American Red Cross. Iron Rich Foods. National Heart, Lung, and Blood Institute. Iron-deficiency anemia. National Heart, Lung, and Blood Institute. Polycythemia Vera. By Amber J. Tresca Amber J. Tresca is a freelance writer and speaker who covers digestive conditions, including IBD. She was diagnosed with ulcerative colitis at age 16. See Our Editorial Process Meet Our Medical Expert Board Share Feedback Was this page helpful? Thanks for your feedback! What is your feedback? Other Helpful Report an Error Submit By clicking “Accept All Cookies”, you agree to the storing of cookies on your device to enhance site navigation, analyze site usage, and assist in our marketing efforts. Cookies Settings Accept All Cookies